There *IS* a way to go from AHCI to RAID (which is required for RST) without reinstalling Windows, but I don't remember the exact steps. IIRC, it involved changing some registry setting, restarting windows into safe mode, installing the RST drivers and then rebooting back into Windows normally. Then you can carve out an SSD partition to use as cache and enable RST.

It helps reduce boot times a little in a best case, but how often do you reboot?

Just install the HDD and use it.

I would disagree. If you're not gaming or using big applications, RST is actually pretty effective.

The new workstations we got at work are Dell XPS machines, and have a 2TB Seagate and a 32GB SSD for RST caching. Unless I fire up an Adobe application, I never hear the HDD spin up (and it's a noisy thing, so I know when it's running). Day to day Office/web/email stuff runs pretty much exclusively out of the super-duper 32GB SKhynix branded linkAmedia SSD.

I used a Samsung 840 EVO instead of my "main SSD" (an 850 of the same size) in case I wanted to fall back (I'd have a pristine installation.)

Performance isn't terrible, but its worse than I hoped it would be; I backed it with a WD Black 1.5TB drive and only discovered at the end of the process that it was only a SATA II drive. Gonna give it a couple days as I don't feel I've given it a chance for the cache engine to really kick in. (Haven't been home enough to use it enough.) This weekend should tell the tale.